<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }
        
        ul{
            width: 450px;
            height: 300px;
            margin: 100px auto;
            background-color: #666;
            text-align: center;
            line-height: 60px;
        }
        li{
            float: left;
            width: 110px;
            height: 60px;
            margin: 20px;
            border-right: 1px solid #000;
            list-style: none;
        }
        ul li:nth-child(3n){
            border-right: 0;
        }
    </style>
</head>
<body>
    <ul>
        <li>盒子1</li>
        <li>盒子2</li>
        <li>盒子3</li>
        <li>盒子4</li>
        <li>盒子5</li>
        <li>盒子6</li>
        <li>盒子7</li>
    </ul>
</body>
</html>